1. Field of the Invention
The present invention relates to an in-line type fluid pressure sensor, and more particularly to an in-line type fluid pressure sensor, which is connected in-line in a fluid flow circuit of a chemically corrosive fluid or liquid to determine the pressure of the corrosive liquid in flow circulated through the fluid flow circuit.
2. Description of the Related Art
In a semiconductor manufacturing apparatus, an etching process of a semiconductor substrate is conducted using a chemical in liquid form, for example such as a liquid chemical comprising a hydrofluoric acid (HF) solution or the like. In order to supply such liquid chemical to the semiconductor manufacturing apparatus in a smooth manner, an in-line type fluid pressure sensor is incorporated in a liquid chemical's circulation circuit of the apparatus.
In view of harshness in corrosive action of the above liquid chemical, it is required for the in-line type fluid pressure sensor to protect its own fluid pressure receiving surface from such harsh corrosive action of the liquid chemical since the fluid pressure receiving surface of the fluid pressure sensor is exposed to the liquid chemical in operation. Due to this, heretofore various types of a protective or isolation member have been proposed and arranged in the fluid pressure sensor to meet the above requirement. More specifically, such an isolation member thus arranged in the fluid pressure sensor functions to prevent the pressure receiving surface of the sensor from making direct contact with the liquid chemical.
In general, the in-line type fluid pressure sensor is provided with an fluid introduction portion for introducing the object or fluid to be measured therein, wherein the fluid pressure receiving surface of the sensor is disposed in an inner end area of the fluid introduction portion of the sensor and brought into contact with the liquid chemical through the protective or isolation member. For example, the fluid introduction portion of the pressure sensor is constructed of: a hollow portion such as one disclosed in FIG. 3 of Japanese Utility Model Registration No. 2547038; or, a lip such as one disclosed in FIG. 4 of Published Japanese translations of PCT international publication for patent application No. Hei 11-512827 (published: Nov. 2, 1999).
As is clear from these FIGS. 3 and 4 of the prior art an inner wall of the fluid introduction portion of the conventional in-line type fluid pressure sensor is so formed as to be perpendicular to a direction in which the fluid flows in construction; and, the fluid flow circuit, in which the fluid pressure sensor is incorporated, has its fluid flow passage enlarged in cross-sectional area at the site of the fluid introduction portion of the fluid pressure sensor. Due to this, the fluid flow circulating through the circuit tends to stand in flow at the site of the fluid introduction portion of the pressure sensor. Such standing phenomenon in the fluid flow appearing in the fluid introduction portion of the sensor substantially makes it impossible for the in-line type fluid pressure sensor to realize a precise measurement of the fluid pressure in flow of the fluid circulated through the fluid flow circuit.
The other in-line types of conventional fluid pressure sensors are disclosed in the following prior arts, for example: Englund et al., in U.S. Pat. No. 5,693,887, which discloses a non-contaminating pressure sensor module having an isolation member; Englund et al., in U.S. Pat. No. 5,852,244, which discloses a non-contaminating pressure transducer module having an isolation member; Ducci et al., in U.S. Pat. No. 5,869,766, which also discloses a non-contaminating pressure transducer module having an isolation member; Imai in U.S. Pat. No. 6,622,564, which discloses a fluid pressure sensor provided with a diaphragm under which any standing phenomenon of the fluid flow is not observed; Okawa in U.S. Pat. No. 6,640,639, which discloses a fluid pressure sensor provided with a fluid pressure measuring portion composed of a resin; Schnell in U.S. Pat. No. 4,192,192, which discloses a diaphragm seal assembly for use with a fluid pressure responsive instrument; and, Sell et al., in U.S. Pat. No. 4,177,496, which discloses a capacitive type fluid pressure sensor or transducer comprising a pair of thin discs made from an insulator.
As described above, it is difficult for the conventional in-line type fluid pressure sensor to realize a precise fluid pressure measurement of the fluid at the site of the fluid introduction portion of the sensor since the conventional fluid pressure sensor suffers from the fluid flow standing phenomenon or problem appearing at the site of the fluid introduction portion of the fluid pressure sensor.